It has been considered that a function for automatically correcting a time display is added to an analog-display-type time measuring apparatus having a second hand, a minute hand, or an hour hand. This function, which automatically corrects the time display, (hereinafter called an automatic time correction function) periodically obtains the standard time by radio or through a line, and corrects the displayed time so that it matches the standard time. The function is also used for adjusting the time to the current time if a time measuring function is stopped due to a cause such as a flat battery. With such an automatic time correction function being provided, the time display on a watch can be automatically adjusted to the local time at a trip destination, or a very precise time can be always indicated.
In these days, portable time measuring apparatuses, such as a watch, operating with a solar battery or in which electricity is generated by detecting the movement of a user's arm with the use of a weight have been developed. In such a time measuring apparatus which does not use a battery, if an electric power is not obtained from a solar battery or the like, it is considered that power consumption is reduced by stopping the motor for displaying the time and counting the time internally. When the time measuring apparatus uses an automatic time correction function, if the solar battery or the like starts generating electricity, the displayed time can be automatically and accurately adjusted to the current time which is counted internally.
To effectively use the automatic time correction function in an analog-display-type time measuring apparatus, it is preferred that a function for automatically detecting the displayed time be added. To reduce power consumption, the time immediately before the apparatus stops can be stored in internal memory or it is possible that the time being displayed is stored in internal memory and time correction is performed with that stored data. Time correction cannot be performed automatically and precisely, however, if the user changes a hand position with the crown while the apparatus is being stopped, if the contents of the memory is lost due to a flat battery, or if a hand-movement error occurs during fast winding for time correction.
To automatically detect the time currently displayed, for example, in a time measuring apparatus having a second hand for indicating the second, a minute hand for indicating the minute, and an hour hand for indicating the hour, it is required to identify the position where each hand is pointing. To this end, it is possible to use an encoder plate which rotates together with each hand. It is considered that the fourth wheel, the center wheel, and the hour wheel driving the second hand, the minute hand, and the hour hand, respectively, are used as encoder plates. It is required to detect sixty positions for each hand precisely, namely at a pitch of six degrees, in order to identify the positions where the second hand and the minute hand are pointing. Since six-bit positional information is enough for identifying sixty positions, it is considered that the positional information is marked on encoder plates at a pitch of six degrees and the positional information is detected. With this method, however, if one detecting apparatus detects one bit, it is necessary to provide six detecting apparatuses for each encoder plate. The detecting apparatuses are too large to be accommodated into a portable time measuring apparatus such as a watch. On the other hand, it can also be considered that an encoder plate which stores positional information as magnetic information like a magnetic recording medium is used. However, it is practically difficult to accommodate the same mechanism as a floppy disk in a watch in order to detect correct magnetic information, and the watch becomes large and expensive if it is provided. With a mechanism in which information is read while a magnetic recording medium is rotating, it is impossible to detect the position where a hand such as an hour hand that moves at a low speed stops.
Accordingly, it is an object of the present invention to provide a position detecting apparatus for detecting an absolute position with a precision of a pitch of six degrees or less by the use of a compact, simple mechanism which can be accommodated into a compact, portable apparatus such as a watch, and a position detecting method therefor. Another object is to provide a compact position detecting apparatus for detecting an absolute position precisely within a short period of time with a simple configuration and a position detecting method therefor.